Wet process of extracting silver from its haloid salts.



UNITED STATES PATENT OFFICE.

LUDIVIG VANINO, OF MUNICH, GERMANY.

WET PROCESS OF EXTRACTING SILVER FROM ITS HALOID SALTS.

SPECIFICATION forming part of Letters Patent No. 630,951, dated August15, 1899.

Application filed January 21, 1899. Serial No. 702,973. (No specimens.)

To all whom it may concern.-

Be it known that I, LUDWIG VANINO, doctor of philosophy, residing atMunich, in the Kingdom of Bavaria, German Empire, have invented certainnew and useful Improvements in WVet Processes of Extracting Silver fromits Haloid Salts; and I do hereby declare the following to be a full,clear, and exact description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame.

The present invention relates to the extraction of silver from itshaloid salts, more particularly from its solid haloid salts by the wetway, and has for its purpose to do away with the technicalinconveniences the extraction of silver from its solid haloid salts bythe wet way as presently operated is accompanied with.

Many methods have been proposed for reducing solid haloid salts ofsilver to metallic silver by the wet way. For instance, metallic silvercan be obtained by bringing together chlorid of silver and zinc or ironin weaklyacidulated water, or by boiling humidified chlorid of silvertogether with sugar, honey, dextrine, or other carbohydrates and sodiumcarbonate, or by digesting chlorid of silver with sugar and potassiumhydroxid. Either of those and the other known methods is defective inthat the reduction takes place but imperfectly; that this imperfectreduction requires a comparatively long space of time; that, moreover,to obtain this imperfect result the assistance of heat is required, andthat the silver is not obtained in a sufficiently pure state, butrequires to be purified by special operations. I have discovered thatformic aldehyde behaves as a very powerful reducing agent towardinsoluble or solid haloid salts of silver also, provided it be caused toact in the presence of a solution of an alkaline agent, such as thehydroxids and carbonates of alkaline and alkalineearth metals. Underthat condition the reducing power of formic aldehyde is such that theconversion, for instance, of solid chlorid of silver into metallicsilver takes place in the cold and then requires but a few minuteswithout leaving any trace of undecomposed chlorid.

My invention consists in the use of this discovery of mine for operatingthe wet extraction of pure metallic silver from its solid haloid salts.

In carrying out the invention, I mix the haloid salt-for instance, solidchlorid of silver-with a solution of one or more of said alkalineagents, preferably with a solution of sodium hydroxid, and to thismixture I add a watery solution of formic aldehyde, operating in thecold. The reduction begins at once and is quantitatively complete aftera few minutes.

A modification consists in passing formicaldehyde vapors into themixture of solid chlorid of silver and alkaline lye, the mixture beingstirred. The silver deposit is separated from the lye and freed fromadhering formic aldehyde and alkaline lye by mere washing with water andthen proves to be of an extraordinary degree of purity.

The important industrial advantage of my wet process as compared withthe older wet methods consists in that the entire quantity of silverpresent in the salt treated is obtained in the state of perfectly puremetal and so in the cold and with great saving of time.

That I claim as my invention is-- The wet process of extracting silverfrom its insoluble haloid salts, which consists in mixing said haloidsalts with a watery solution of alkaline agents, and adding formicaldehyde in the cold, substantially as and for the purpose specified:

In testimony whereof I affix my signature in presence of two witnesses.

LUDWIG VANINO.

lVitnesses EMIL HENZEL, RiiDoLE DIEM.

